The following references to and descriptions of prior proposals or products are not intended to be, and are not to be construed as, statements or admissions of common general knowledge in the art. In particular, the following prior art discussion does not relate to what is commonly or well known by the person skilled in the art, but assists in the understanding of the inventive step of the present invention of which the identification of pertinent prior art proposals is but one part.
For ease of description, we shall refer to such a spray nozzle assembly in terms of one associated with spray drying of milk.
In general, spray nozzles that are provided with swirl chambers and orifice discs have these components manufactured from tungsten carbide or the like, which is very hard, but also brittle and prone to damage when dropped or otherwise roughly treated during assembly and disassembly.
When ordinary spray nozzles are used for spray drying milk, a certain percentage of the liquid simply falls as drops from the nozzles, without being atomized, and this material can well lead to spoiling of the product.
To avoid this problem, a unitary check valve was developed for spray drying nozzles, and other nozzles, which caused little restriction in the flow through the nozzle and which, at the same time, did not have any parts, or break-off parts thereof, likely to be passed into the fluid stream.
Conventional check valves, however, have sealing problems when operated at high pressures and are not necessarily as compact as would be desirable.
Prior art nozzles generally have stepped annular shoulders that ensure coaxial alignment and concentricity of respective, axially aligned wear parts. However, because the flow material (like proteinous milk products) can set or dry to a viscous or glue-like consistency, it is necessary to build in clearance gaps including radial gaps (lateral gaps to the side of the wear parts) or axial gaps (longitudinal gaps between the wear parts and the nozzle components axially containing them). These gaps between the wear parts and the nozzle cylinder need to provide sufficient play or movability of the respective parts relative to each other to facilitate removal for replacement, cleaning and repair. Also, normal manufacturing tolerances dictate a gap requirement to prevent component jams axially and radially. Therefore, the prior art designs inherently lack accurate concentricity, which has adverse affects on spray nozzle performance, predictability of spay patterns and/or spray line production. Stepped annular shoulders in the internal wall of the nozzle cap mean prior art caps are structurally weak and introduce stress concentrations at the sharp angled corners within these steps.